Reproduction performances and conditions of group-housed non ...

- Paper I -
pregnancy failure. There is a negative correlation between feed intake during gestation and
feed intake during lactation, for which reason very high feed intake during gestation may
lead to low energy intake in lactation and thereby perhaps a lower litter size and pregnancy
rate in the following cyclus. However, how high the feed intake in pregnancy shall be be-
fore reproduction in the next cyclus is impaired, is not possible to say.
5. Discussion
The results reviewed do not provide a clear picture of the relation between energy supply
and reproduction in female pigs because the results are often inconsistent. It is therefore
difficult to draw unambiguous conclusions, however, some lines can be drawn.
First of all, it seems that the reproduction performance of gilts in general is more influenced
by energy supply than the reproduction performance of the sow. There are indications that
ovulation rate and thereby litter size can be impaired in gilts if they are fed restricted (≤25
MJ ME day -1 ) before mating. When it comes to the sow, the picture is much less clear.
Energy intake from weaning to mating seems to have little influence on litter size although
moderate energy intake (37 compared to 74 MJ ME day -1 ) did impair litter size in sows that
experienced severe weight loss (39 kg) during lactation in one study (Baidoo et al., 1992).
There are indications that litter size in gilts can be reduced if they are fed moderate (≥31 MJ
ME day -1 ) compared to low (18-23 MJ ME day -1 ) level of energy the first three days after
mating. Whether this is also the case for the sow has not been confirmed. The number of
born piglets per litter seems to be highly resistant to even starvation in early pregnancy in
some female pigs, however, there are indications that very low energy intake (≤13 MJ ME
day -1 ) the first four weeks in pregnancy may impair litter size. Less restricted energy intake
(21 MJ ME day -1 ) in early pregnancy may also reduce the litter size in sows fed very restricted
(36 MJ ME day -1 ) during lactation. Pregnancy rate in gilts can apparently be reduced
if they are fed very restricted (≤18 MJ ME day -1 ) the first 35 days of pregnancy.
Whether this is the same for sows is not possible to conclude, however, it seems that low
energy intake for several successive parities can increase the risk of being culled as a consequence
of not being pregnant. Furthermore, it cannot be excluded that high feed intake
during pregnancy reduces voluntary feed intake in lactation and thereby reduce the litter
size in the following cyclus.
The existence of a relation between energy intake and litter size and pregnancy rate is further
supported by studies showing an effect of energy related hormones, e.g. insulin and
IGF-1, on the hormonal control of litter size and pregnancy. The increase in ovulation rate
seen in gilts as a consequence of flushing before oestrus is thus believed to be mediated
through an increase in insulin and IGF-1 levels followed by an increase in plasma levels of
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